ENH: Protect fiona imports so that they are not required at module level

geopandas/geodataframe.py

@@ -7,7 +7,6 @@ import json
 import os
 import sys
 
-import fiona
 import numpy as np
 from pandas import DataFrame, Series
 from shapely.geometry import mapping
@@ -245,6 +244,7 @@ class GeoDataFrame(DataFrame):
         The *kwargs* are passed to fiona.open and can be used to write 
         to multi-layer data, store data within archives (zip files), etc.
         """
+        import fiona
         def convert_type(in_type):
             if in_type == object:
                 return 'str'

geopandas/geoseries.py

@@ -1,8 +1,6 @@
 from functools import partial
 from warnings import warn
 
-import fiona
-from fiona.crs import from_epsg
 import numpy as np
 from pandas import Series, DataFrame
 import pyproj
@@ -74,6 +72,7 @@ class GeoSeries(Series):
             etc.
         
         """
+        import fiona
         geoms = []
         with fiona.open(filename, **kwargs) as f:
             crs = f.crs
@@ -616,6 +615,7 @@ class GeoSeries(Series):
         projection, not geodesics.  Objects crossing the dateline (or
         other projection boundary) will have undesirable behavior.
         """
+        from fiona.crs import from_epsg
         if self.crs is None:
             raise ValueError('Cannot transform naive geometries.  '
                              'Please set a crs on the object first.')

geopandas/io/file.py

@@ -1,7 +1,6 @@
 from collections import defaultdict
 
 from shapely.geometry import shape
-import fiona
 
 from geopandas import GeoSeries, GeoDataFrame
 
@@ -17,6 +16,7 @@ def read_file(filename, **kwargs):
     Properties that are not present in all features of the source
     file will not be properly aligned.  This should be fixed.
     """
+    import fiona
     geoms = []
     columns = defaultdict(lambda: [])
     bbox = kwargs.pop('bbox', None)